1981 Pac Man Video issue

5thcorps

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Hello all and thanks for a fantastic forum. Just acquired a 1981 Pac Man upright arcade game which has a couple intermittent issues. I've been looking extensively online for a similar problem but haven't found one yet posted anywhere. The minor issue is once turned on it seems to jumble a bit with a few different symbols before freezing like that. Turning it off then back on usually takes care of it by the second try. The other issue may be related. After playing for a few minutes the charactors disappear and the maze is all fuzzy then the charactors start to show up hazy and usually out of line with the maze. The sound is not disturbed and if you move the joystick it will still move and eat the dots. It will suddenly go back to normal for a minute then return to the poor condition. Unsure what's going on here because like I said it comes and goes multiple times per level. Then may run normal for an entire level before acting up again. Any ideas are EXTREMELY appreciated.
 
Here is a still view of the problem. Also noticce the blue vertical lines but slightly slanted all the way on the left
PACMAN005b.jpg
 
Just one more note, when going awry the moving pacman moves up to the left corner as if the whole maze was moved but it is not of course. it runs thru the walls up there. Almost liek its not mapping correctly.
 
Is it possible to swap chips that are the same on the board to see if the problem changes or goes away?
 
If you havent already, reseat all the ROMs and the 2 daughter cards to make sure they are all making a good connection. It also looks like the brightness on your monitor is turned up a little too high.
 
Check your +5 volts and then clean the legs on all socketed chips and reseat them. Get rid of the RF interface board if its still there.
Sorry to sound like a total noob, (I'm a mechanic just getting into other kinds of electronics)
But is there a main +5 I need to check, or check it at all points, ie each chip?
And are the chips that are numbered the same interchangable for the purpose of swapping them around to check for problem chips?
 
The chips are only swappable with one of the exact same kind. For example, a ROM at 5E needs to be replaced with another chip from 5E of a different board with the same game. I suggest swapping chips be the last thing you try unless you have another working board available.

As for the +5, you need to check it at the edge connector of the board. I am not sure what pin, but ArcRevival can help you with that. Also like AR said, if there is a filter board between the game board and the edge connector, remove it and plug the connector directly into the game board, as filter boards are a great source of many problems.
 
to explain..

Pacs came with a small finger RF board between the pcb board and the main wiring harness.. you can take it out and connect the harness direct. If there is not a RF board.. take the wiring harness off and put it back on to get a better connection.

yes, take out all the socketed chips..one at a time.. and note which direction they came out.. carefully !

clean any rust / crude on the legs carefully, and put back in.

Also, as mentioned... the brightness on your monitor is a bit too high.. look for the brightness control on the monitor back and turn it down some..

pics and vid's are helpful... of your pcb board and back of the monitor and we can point out where you need to look.

The +5 can be checked with a digital multi meter.... on the pcb board.. if it is too low... it can cause weird problems.. but should be too high either..
 
No RF board, harness plugs directly into main board. So I take it that the chips that are the same must hold some kind of memory of their respective positions after originally being placed? What do you guys clean the prongs with?
 
yes chips go exactly back in same socket.. facing the same way!

some say dont do it.. but I use fine sandpaper and light scuff the chip legs to clean them up..

be careful taking the chips out.. pry both sides evenly so you dont bend and break legs off.. which is common..

good news.. you can get new chips for it easily...

after cleaning the legs.. re seat them in the sockets firmly...

do this with every socketed chip... same for any 'daughter' boards' coming off of the main board...
 
As for the +5, you need to check it at the edge connector of the board.

Not correct, its AC at the edge connector. Set your meter to DC volts and measure across capacitor C3. You should get 5v +/- .2 or so.
Doesnt look like a voltage issue to me.
 
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The brightness it to high as stated..you should have a black backround and you might have issue with your character Prom chips...
Could be dirty..loose sockets..or need replacing..Check 5F to start
 
Checked, cleaned, and reseated all chips. all fine. +5 volts across both caps checks good. Problem comes for a long time then goes away for a short time. earlier today I was able to move the wire harness and get it to act up and clear up at will. then it stopped doing that and has been acting up for the rest of the time now. No broken wires from what I see, ground appears to be fine. Any thoughts?
 
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